Electric refrigeration and air-conditioning protection circuit

ABSTRACT

An electric refrigeration compressor protection circuit to prevent restarting of the compressor motor until after a predetermined minimum time after each stopping of the compressor motor comprising a timer motor and timer switch having its contacts in series with the room thermostat, compressor overload switches and the energizing coil of a compressor contactor switch in a low voltage control circuit and with means responsive to the energization of the compressor motor to stop the timer motor and with the timer contacts arranged to be normally opened but closed only momentarily at spaced time intervals during operation of the timer motor.

United States tet Inventor Roger F. Chesebro Bay Village, Ohio Appl. No.867,320

Filed Oct. 17, 1969 Patented June 8, 1971 Assignee Fraser & JohnstonCompany San Lorenzo, Calif.

ELECTRIC REFRIGERATION AND AIR- CONDITIONING PROTECTION CIRCUIT PrimaryExaminer-Meyer Perlin A!t0meysF. H. Henson and F. E. Blake ABSTRACT: Anelectric refrigeration compressor protection circuit to preventrestarting of the compressor motor until after a predetermined minimumtime after each stopping of the compressor motor comprising a timermotor and timer switch having its contacts in series with the roomthermostat, compressor overload switches and the energizing coil of acompressor contactor switch in a low voltage control circuit and withmeans responsive to the energization of the compressor motor to stop thetimer motor and with the timer contacts arranged to be normally openedbut closed only momentarily at spaced time intervals during operation ofthe timer motor.

COM PRESSOR PATENTEDJUH 8197i 3583.173

COMPRESSOR u FIG.2 c g l8 l9 I 2: lo l6 H3] 21 I5 26 [F COMPRESSOR f7 2423 25 I 22 l 1 l l INVENTOR Roger F Chesebro ATTORNEY ELECTRICREFRIGERATION AND AIR-CONDITIONING PROTECTION CIRCUIT CROSS-REFERENCESTO RELATED PATENT APPLICATIONS BACKGROUND OF THE INVENTION Protectivecircuits for electric refrigeration and air-conditioning systems arewell known and they often employ a form of timing device to preventimmediate restarting of the compressor until after a predetermined timeinterval during which the system pressures can equalize. In recent yearsthe timing device has been in the form of a timer motor switch whichruns either intermittently or continuously. In any event, the timerswitch contacts are subject to considerable usage and it is thereforedesirable to provide the most simple and reliable timer switch contactstructures as possible. Also, the application of the timer switchcontacts in the protection circuit should be such as to minimize theirperiods of operation and also minimize the possibilities of arcing andwelding of the contacts during operation so as to prolong the life ofboth the timer switch contacts and the timer motor.

DESCRIPTION OF THE PRIOR ART Reference may be made to the followinglisted U.S. Pats. which disclose prior arrangement of timer switches inthe protection circuits for electric refrigeration or air-conditioningcompressor motors:

No. 2,276,369 to Buchanan, issued Mar. l7, I942;

No. 2,967,977 to McNicol et al., issued Jan. I0, I961;

No. 3,054,271 to McGrath et al., issued Sept. 18, 1962.

SUMMARY OF THE INVENTION In accordance with the present invention. thetimer switch contacts which are normally open but momentarily closed atspaced time intervals while a timer motor connected thereto is running,are connected in the low voltage control circuit in series with thecontrol switch or thermostat, the normally closed overload switches, andthe compressor contactor switch coil. The timer motor is connected to beenergized and operated only when the compressor motor is not energizedand operating and for such purpose a simple relay with normally closedcontacts in series with the timer motor and a source of current may beconnected with its operating coil in parallel with the compressor motoror in such other circuit arrangements as would be responsive to theenergization of the compressor motor to stop the running of the timermotor. Thus the compressor contactor switch can be closed and thecompressor motor energized only when all of the thermostat, timer switchand overload switches are enclosed. It will be noted that the timermotor is at the same time stopped while the compressor motor is running.Thereafter, when the compressor motor stops due to the opening of eitherthe thermostat or overload switches, the timer motor restarts to openthe timer switch and to prevent the restarting of the compressor motoruntil after the lapse of at least a predetermined minimum time intervalwhen the timer switch contacts may be again momentarily closed. Sincethe timer motor runs only when the compressor motor is not running andsince the timer switch contacts are simple single-pole make and breakcontacts connected in the low voltage control circuit, long timer switchlife with a minimum chance of switch contact arcing and welding isassured.

Further features and advantages of the invention will be apparent withreference to the following specification and drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. II is a schematic wiring anddiagram of the preferred form of the invention with the switch contactsshown in the positions assumed when the compressor motor is not runningand the timer motor is running;

FIG. 2 is a schematic wiring diagram similar to FIG. 1 but showing theswitch contacts in their positions assumed when the compressor motor isrunning and the timer motor is not running; and

FIG. 3 is a fragmentary schematic wiring diagram showing a modified formof the invention in which the timer motor is energized from the lowvoltage source instead of from the high voltage source as shown by FIGS.1 and 2 of the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. I and 2 ofthe drawing, the compressor motor I0 is adapted to be connected andenergized to be operated from the high voltage source terminals 11 and[2 whenever the contactor switch contacts 13 and 14 are closed upon theenergization of the contactor coil IS. The contactor coil 15 isconnected to be energized from the low voltage control source atterminals 16 and 17 through a series circuit including normally closedoverload switch contacts 18 and 19 and normally open timer switchcontacts 20. The thermostatic control switch 21 is also connected in theseries circuit including the timer switch 20 and the overload switches18 and 19. The normally opened timer switch contacts 20 are periodicallyand momentarily closed at spaced time intervals in response to therotation of the switch actuating cam 22 which causes the cam projection23 to reciprocate the switch contact operating rod 24 upwards tomomentarily close the switch contact 20.

The timer cam 22 is rotated by the operation of the timer motor 25 whichmay be connected to a suitable source of current through the normallyclosed relay contacts 26. As shown by FIGS. I and 2 of the drawing thetimer motor 25 is connected through the normally closed relay contacts26 to the high voltage source terminals II and 12 but in the modifiedform of the invention shown by FIG. 3 of the drawing the timer switchmotor 25 is connected through the normally closed contacts 26 to the lowvoltage source terminals 16 and I7. Either arrangement of connection forenergizing the timer motor 25 may be used depending upon the desiredoperating voltage for the timer motor 25.

The normally closed relay contacts 26 are connected to be openedwhenever the relay coil 27 is energized and the relay coil 27 isconnected in parallel with the compressor motor 10 so as to be energizedsimultaneously therewith whenever the contactor coil 15 is energized toclose the contact switches 13 and I4 and energize the compressor motor10. Thus the timer motor 25 is connected to be running only when thecompressor motor 10 is not running and vice versa. Although a simplecircuit including the relay coil 27 and normally closed relay contacts26 has been specifically shown for purposes of preventing the operationof the timer motor whenever the compressor motor 10 is running, itshould be obvious that various other circuit arrangements known to thoseskilled in the art could be used to obtain the desired function of thetimer motor 25 to be running whenever the compressor motor 10 is notrunning.

The operation of the protective circuit of the invention will now bedescribed again with reference to FIGS. 1 and 2 of the drawing. When thecontrol switch or thermostatic switch 21 is closed because of a demandfor refrigeration or cooling as shown by FIG. 2 of the drawing, thecompressor contactor coil 15 can be energized only when the normallyclosed overload switches 18 and 19 are also closed and the timer switchcontact 21 is momentarily closed. At such time with the compres sorcontactor coil 15 thus energized, the contactor switches 13 and 14 willclose to energize both the compressor motor 10 and the relay coil 27 toopen the normally closed relay contacts 26 and stop the timer motor 25with the cam 23 holding the timer switch contacts 2] closed. Thereafterthe compressor motor 10 may continue to run until such time as eitherthe thermostatic control switch 21 opens or, in the event of trouhle, anoverload switch contact l8 or l9 may open. When any of the switches l8and I) or 2| open to deenergize the compressor contaetor coil 15 andopen the contaetor switches 13 and I4 to stop the compressor motor 10,the relay coil 27 will he deenergized to close its normally closed relaycontacts 26 and again start the timer motor 25 to run thus opening thetimer switch contact 20 as shown by FIG. I of the drawing. Shouldthereafter either the thermostat control switch 21 or the overloadswitches 18 and 19 immediately reclose such as might occur by achattering of thermostat switch contacts or by unusual operation of theoverload switches l8, 19, the compressor motor can nevertheless notimmediately restart because the timer switch contacts 20 have opened andremain open while the timer motor 25 is running until the timer contactoperating cam 23 again reaches the position shown by FIG. 2 of thedrawings to momentarily reclose the timer contact switch 20. l havefound that a suitable time interval of about 6 minutes for a singlerotation of the timer switch cam 22 will assure equalization of thesystem pressures before the contaetor coil can again be energized toclose the contactor switches l3, l4 and rcoperate the compressor motor10. However, this invention is not limited to any predetermined minimumtime between the momentary closures of the timer switch while the timermotor 25 is operating.

It should now be understood that a simple and reliable protectivecircuit is obtained in that the timer switch contact 20 is a simplesingle-pole make and break switch operating in a low voltage circuitwhere there will be a minimum possibility for contact arcing andwelding. In addition the arrangement of the invention wherein the timermotor 25 is operated only when the compressor motor 10 is not operated,minimizes the duty cycle for the timer motor 25 so as to obtainextremely long motor lifetime in application.

Various modifications will occur to those skilled in the art.

l claim as my invention:

1. A control circuit for a refrigeration system having an electric motordriven refrigerant compressor comprising, a first source of relativelyhigh voltage, electric current adapted for energizing said compressormotor, a second source of relatively low voltage electric currentadapted for control purposes, a contaetor having normally open contactsand a coil to be energized to close its normally open contacts, meansconnecting said compressor motor in series with said normally opencontacts to said first source, a control switch and a normally opentimer switch connected in series with said second source and saidcontaetor coil to energize said contaetor coil when all of said switchesare closed, an electric timer motor,

means responsive to connect and energize to operate said timer motorfrom one of said sources only when said compressor motor is notenergized, and means connecting said timer motor shaft to said timerswitch in a manner to momentarily close said normally open timer switchat predetermined spaced time intervals during operation of said timermotor whereby to energize said contaetor coil and said compressor motorwhen both said timer and control switch are closed, said timer motorbeing subsequently reenergized to open said timer switch and prevent asubsequent reenergization of said contaetor coil and compressor motoruntil at least a predetermined time interval after said compressor motorhas been deenergized responsive to opening of any of said seriesconnected switches.

2. The invention of claim 1 in which the means responsive to energizeand operate said timer motor is a relay having a coil connected to beenergized by the energizing circuit for said compressor motor, saidrelay having normally closed contacts connected in circuit with saidtimer motor and said first source of electric current to therebyenergize said timer motor only when said compressor motor and said relaycoil are deenergized.

3. The invention of claim 2 in which at least one compressor overloadresponsive normally closed switch is connected in the series circuitwith said control switch and said timer switch.

4. The invention of claim 1 in which the means responsive to energizeand operate said timer motor is a relay having a coil connected to beenergized by the energizing circuit for said compressor motor, saidrelay having normally closed contacts connected in circuit with saidtimer motor and said second source of electric current to therebyenergize said timer motor only when said compressor motor and said relaycoil are deenergized.

5. The invention of claim 4 in which at least one compressor overloadresponsive normally closed switch is connected in the series circuitwith said control switch and said timer switch.

6. The invention of claim 1 in which at least one compressor overloadresponsive normally closed switch is connected in the series circuitwith said control switch and said timer switch.

7. The invention of claim 6 in which said control switch is athermostatic responsive control switch.

8. The invention of claim 1 in which said control switch is athermostatic responsive control switch.

1. A control circuit for a refrigeration system having an electric motordriven refrigerant compressor comprising, a first source of relativelyhigh voltage electric current adapted for energizing said compressormotor, a second source of relatively low voltage electric currentadapted for control purposes, a contactor having normally open contactsand a coil to be energized to close its normally open contacts, meansconnecting said compressor motor in series with said normally opencontacts to said first source, a control switch and a normally opentimer switch connected in series with said second source and saidcontactor coil to energize said contactor coil when all of said switchesare closed, an electric timer motor, means responsive to connect andenergize to operate said timer motor from one of said sources only whensaid compressor motor is not energized, and means connecting said timermotor shaft to said timer switch in a manner to momentarily close saidnormally open timer switch at predetermined spaced time intervals duringoperation of said timer motor whereby to energize said contactor coiland said compresSor motor when both said timer and control switch areclosed, said timer motor being subsequently reenergized to open saidtimer switch and prevent a subsequent reenergization of said contactorcoil and compressor motor until at least a predetermined time intervalafter said compressor motor has been deenergized responsive to openingof any of said series connected switches.
 2. The invention of claim 1 inwhich the means responsive to energize and operate said timer motor is arelay having a coil connected to be energized by the energizing circuitfor said compressor motor, said relay having normally closed contactsconnected in circuit with said timer motor and said first source ofelectric current to thereby energize said timer motor only when saidcompressor motor and said relay coil are deenergized.
 3. The inventionof claim 2 in which at least one compressor overload responsive normallyclosed switch is connected in the series circuit with said controlswitch and said timer switch.
 4. The invention of claim 1 in which themeans responsive to energize and operate said timer motor is a relayhaving a coil connected to be energized by the energizing circuit forsaid compressor motor, said relay having normally closed contactsconnected in circuit with said timer motor and said second source ofelectric current to thereby energize said timer motor only when saidcompressor motor and said relay coil are deenergized.
 5. The inventionof claim 4 in which at least one compressor overload responsive normallyclosed switch is connected in the series circuit with said controlswitch and said timer switch.
 6. The invention of claim 1 in which atleast one compressor overload responsive normally closed switch isconnected in the series circuit with said control switch and said timerswitch.
 7. The invention of claim 6 in which said control switch is athermostatic responsive control switch.
 8. The invention of claim 1 inwhich said control switch is a thermostatic responsive control switch.